The field of the disclosure relates generally to leak detection on vessels and tanks, and more specifically, to methods and systems for evaporative cooling infrared thermographic leak detection.
Infrared thermography can be utilized to find leaks in vessels and tanks when the velocity flow through the leakage areas is high enough to impart a temperature change to the surrounding areas. However, in commercial aircraft fuel tank testing, the amounts of pressurization are very low. In these low pressure testing situations, any temperature changes around a leakage area, or in the leakage area itself, may be masked by sealant, the material from which the tank or vessel is built (e.g., aluminum) and the fasteners immediately adjacent to the leak. As a result, in these low velocity areas, infrared thermography on its own is not sufficient to provide a complete solution to leak detection, especially for commercial aircraft fuel tank testing and/or cabin pressurization testing. As a result, traditional leak detection methods using infrared thermography alone are strongly dependant on high velocities at the leakage areas to impart a localized temperature change for detection and high velocities generally require testing under higher pressures.
It is desirable to accomplish leak testing at lower pressures. Therefore, in one current tank testing method, all external seams of the tank are painted with an indicator paint that reacts when in contact with anhydrous ammonia. A fifteen percent anhydrous ammonia/air mixture is then used to pressurize the tanks and any leaks are shown through discoloration of the indicator paint. Leakage areas are then noted and the indicator paint is removed and a repair or refurbishment of the tank is undertaken. In another currently used tank testing method, a five percent helium gas/air mixture is used along with helium detectors to determine the presence of any leakage area associated with the pressurized tank.
One downside to the above described testing methods is the recurring material costs associated with Anhydrous ammonia, helium and the indicators. In the case of anhydrous ammonia, it is also a hazardous substance. The application and removal of the indicator associated with the anhydrous ammonia testing method is an added labor cost as well. Helium is an asphyxiant and side effects are proportional to oxygen displacement. Further, helium detectors do not have the ability to show visualization of leaks but provide only an approximation of where the leaks are.
In contrast to the above leak testing methodologies, evaporative cooling uses the natural relationship between relative humidity, water and air temperature. Relative humidity is defined as the ratio of the actual vapor pressure to the pressure of saturated vapor of air at the prevailing dry bulb temperature. It is thus an indication of the amount of water vapor that can be absorbed by the air until it reaches 100% relative humidity. In the context of evaporative cooling, dehumidified air leaving the one area at a reduced water content (de-humidified to a lower relative humidity value) and moving into an area of higher humidity has the capacity to absorb more water than the surrounding atmosphere thereby producing a localized drop in temperature, and hence the term evaporative cooling.